The invention relates to a process for the wet-chemical metallizing of porous synthetic substrates.
The porous synthetic substrates of the type addressed here consist of a plurality of fibers, which are woven to one another, glued to one another or otherwise appropriately connected with one another. Alternatively, the porous substrates are formed of walls of open, mutually communicating pores. Porous synthetic substrates of this type are used for filtering, insulating or for various collecting or retaining purposes. Polyolefins, polyamides, polyesters, polyphenylene sulfides, or other polymers can be used as the basic substrate materials as porous nonwovens, open-pore foams, or woven felts.
For many technical applications, coating the electrically non-conductive fiber surfaces or pore wall surfaces with a thin metal layer is recommended. This can take place by means of physical processes, such as the depositing of physical vapor (PVD) or chemical vapor (CVD) or by wet-chemical methods. In a wider sense, the invention relates to the wet-chemical metallizing of fiber surfaces or pore wall surfaces of porous substrates.
The wet-chemical metal depositing normally provides that the surface of the porous synthetic substrate:
first be correspondingly conditioned, which can take place, for example, by etching, by roughening as the result of glow discharge, by partially dissolving, by coating with a hydrophilic substance, among other methods; PA1 subsequently, a precious-metal-containing, catalytically active compound is deposited on the conditioned surface, for which a Pd/Sn-compound is frequently used; however, in principle, silver compounds or platinum compounds can also be used; and PA1 finally, after the removal of the spent activating solution, which contains catalytically active particles, from the pores of the porous substrate, the activated surface of the fibers or pores is brought in contact with a metallizing solution and thereby is chemically metallized. PA1 the conditioning, PA1 the activating, PA1 the removal of the spent activating solution from the pores of the substrate, PA1 the chemical metallizing, PA1 the removal of the spent metallizing solution from the pores of the substrate, and PA1 applicable rinsing operations for removing salt or metal residue from the chemical metallizing solution from the pores of the substrate, have different limitations for the process as a whole, such as a limitation on reaction times. PA1 saturating the substrate with a Pd/Sn activating solution; PA1 removing the spent activating solution; PA1 saturating the substrate with a chemical metallizing solution; PA1 removing the spent chemical metallizing solution; PA1 washing the substrate with water; and PA1 removing the water. PA1 a saturation station comprising an activating solution based on a Pd/Sn solution, PA1 a station that removes the spent activating solution, PA1 a saturation station comprising a chemical metallizing solution, PA1 a station that removes the spent chemical metallizing solution, PA1 a water wash station, and PA1 a station that removes the washing water. PA1 the concentration of the solution components, PA1 the temperature of the activating and/or metallizing solution, PA1 the type of the activating solution used or the extent of activation of the fiber surface or pore wall surface of the porous substrate.
Relevant literature concerning the state of the art is found, for example, in the publication "Kunststoff-Galvanisierung" ("Electrometallizing Plastics"), "Handbuch fuer Theorie und Praxis" ("Manual for Theory and Practice"), Leuze Publishers, Saulgau/Wuertt.), or in citations from German patent literature, such as German Patent Documents DE 39 25 232 C2, DE 36 31 055 C2, DE 40 33 518 C2, DE 42 42 443 C2, DE 38 43 903 C2, DE 39 14 726 C2, DE 37 10 895 C2 or DE 36 37 130 C2.
From the above-mentioned state of the art, metallizing conditioned nonwoven, woven felt or opened-pored foam webs, involves saturating with an activating solution, preferably one based on Pd/Sn; then removing the spent activating solution from the pores of the porous substrate; and finally a chemical metallizing solution is brought in contact with the substrate surface. Preferably, copper and nickel are deposited as the metals; however, other metals can naturally also be deposited. As required, the chemically deposited metal layer can subsequently be reinforced galvanically with the same or a different metal.
Because of their fundamentally different individual functions, the individual process steps, specifically,
The conditioning for imparting hydrophilic characteristics to the fiber or pore wall, for example, by saturating with a wetting agent and letting a wetting agent evaporate, may, under certain circumstances, take hours.
Activating with an acidic, freshly produced activating solution, based on Pd/Sn, takes between 5 and 15 minutes.
Removing spent activating solution from the pores of the substrate, depending on the porosity, takes 15 to 20 minutes.
Coating the activated fiber surfaces or pore wall surfaces with a metal layer takes 20 to 30 minutes. And rinsing with inflow water takes 2 minutes.
Finally, the mechanical removal of the rinsing water, at substrate porosities of 45 to 95%, takes another 15 to 20 minutes.
A complete successive linking of these different process steps into a uniformly continuous metallizing process, for porous substrates with starting porosities of from 45 to 95%, has not been implemented because of the different treatment times required. German Patent Document DE 41 06 696 C2, in the manner of a starting point, that is, for a partial activation, shows a possibility of a continuous method of operation. There--as customary--the conditioning of the substrate surface is included in the manufacturing process of the porous substrate. According to the state of the art, the porous substrate webs are continuously activated by means of a Pd/Sn-solution in a so-called one-step process. The continuous process sequence is limited to only saturating with an activating solution followed by a two-step drying process. The subsequent chemical metallizing is again carried out in batch quantities. Thus, only a part of the different process steps needed for wet-chemical metallizing of porous substrate webs is carried out in a continuous manner. Difficulties occur also as the result of the high-expenditure of time and effort and the two-step removal of the spent activating solution from the pores of the substrate. A two-step removal is used because the carried-through air quantities charged with hydrochloric acid particles can be detoxified only in a laborious, second step.
In the case of the state of the art, the removal of the spent metallizing solution from the pores, and the rinsing operations that must follow, cannot easily be included in a continuous sequence of the overall metallization process. In addition, control of hot-air drying requires high expenditures of time and effort in order to avoid local migration effects of catalytically ineffective Pd.sup.2+. Once the continuous process sequence of the metallizing operation is interrupted in favor of a batch-type mechanical removal of spent metallizing solution or for rinsing water from the pores of the substrates, additional subsequent steps are required. This results in increased handling expenditures and higher labor cost.
The invention provides a more effective process for metallizing porous substrate webs made of a non-conductive synthetic material. The process is amenable to continuous operation, without interruptions, so that an entire metallizing function is performed.
The invention comprises the mutual coordination of the reaction rates during the activating and the chemical metallizing steps. The targeted selection and combination of the parameters of the activating solution and of the metallizing solution and of the intermediate removal of the respective spent reaction solutions from the pores of the porous substrate, as a whole, permits a continuous method of operation. Thus, the substrate may advance through all treatment stations, which performs all the steps of metallizing, in a uniform speed. Because of the invention, continuously operating and low-cost chemical metallizing can be implemented on an industrial scale with relatively low control requirements, low regulating expenditures, and low labor costs.
The surprising aspect of the invention is the fact that, while the process solutions, specifically the activating solution and the metallizing solution, are uniformly charged to the surface of the fibers or pores along the thickness of the material, it is possible to adapt the reactions to allow uniform reaction times at each step. The adsorptive activation, by means of precious-metal-containing (Pd/Sn) activating solutions, and the chemical metallization (nickel-plating, copper-plating or similar methods) occur at different reaction rates. However, by adapting the parameters of these reactions, for example selecting a concentration or a specific type of active substance, as well as an appropriate temperature for each reaction or step, a uniform time at each step in the process can be determined. Thus, modifying parameters with respect to the reaction rate for each step allows the substrate web to be guided continuously through no more than six stations. Simultaneously, the mechanically stressful suction to remove the spent process solutions is included in the process sequence.
The invention provides a process for the wet-chemical metallizing of porous substrates. Generally, the substrates have porosities of between 45 and 95% and comprise a non-conductive synthetic material, such as woven felts, nonwovens, or open-pored foams. In the process, the fiber surfaces or pore walls of the substrate are first activated by means of a Pd/Sn-containing activating solution. The activated surfaces are then metallized by means of a metallizing solution and are finally rinsed and freed of rinsing water. Furthermore, the invention involves hydrophilic or hydrophilized substrates being guided at an advancing speed, which is the same for all treatment stations, as a cohesive web and in a continuous process sequence, through a succession of treatment stations that result in a metallized substrate. The treatment stations comprise the steps of:
The dwelling time of the substrates in the respective treatment stations can be optimized or varied depending on a number of parameters. A short saturating step can be compensated by the selection of the treatment liquid, specifically the concentration and/or the temperature. Selecting the treatment liquid allows an acceleration of the reaction in such a manner that, because of the reaction times actually implemented in a treatment station, continuous passage of the substrate is permitted. Generally, the spent treatment liquids, specifically the activating solution, the chemical metallizing solution, and the adhering rinsing water, are removed by suction from the pores of the porous substrate.
In specific embodiments, a nickel-plating solution is used as the chemical metallizing solution, which in addition to a dissolved nickel salt, contains only a chemical reduction agent but no additional electrolytes, such as pH-regulators, completing agents, or other stabilizers. To accelerate the metallizing reaction, the metallizing solution can be heated to a temperature of approximately 60.degree. C.
In another embodiment, the rate of the activating reac tion is accelerated by raising the temper ature of the activating solution to 30 to 35.degree. C.
In further embodiments, the invention provides nickel-plated substrates made by the chemical metallizing processes, as well as other Substrates made by the processes, and metallizing solutions employed in the processes.
Although the invention has been described and illust rated in detail, it is to be clearly understood that the same is by way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.